Our goal is to explore novel tumor suppressor mechanisms dependent on the integrity of primary cilia. Our preliminary data shows the absence of cilia in cholangiocarcinoma cells; therefore, ciliary dysfunction may be associated with cancer development. The mechanisms leading to ciliary reduction in these tumor cells as well as the consequences of such a lost remain unknown. We HYPOTHESIZE that the functional integrity of cholangiocyte primary cilia is required for the transduction of environmental stimuli, and generates intracellular signals that function as tumor suppressors. We propose that in cholangiocarcinoma, (i) decreased microRNAs expression (i.e. mir-433, mir-22, mir-141, mir-200) leads to overexpression of HDAC6, a cytoplasmic deacetylase that induces ciliary resorption, and the subsequent reduction of cholangiocyte primary cilia; and (ii) ciliary loss generates the disengagement between the environment and the cell interior resulting in derepression of tumorigenic factors and cancer development. In Specific Aim #1 we will characterize the effect of ciliary loss on the normal cholangiocyte phenotype. Our working hypothesis, based upon preliminary data, is that primary cilia and the intracellular signals induced by their multisensory functions are constraining Hedgehog and MAPK pathways, which are involved in cancer development. In Specific Aim #2 we will characterize the effect of specific miRNAs downregulated in CCA on cholangiocyte ciliary expression. Our working hypothesis is that the downregulation of mir-433, mir-22, mir-141, and/or mir-200 in CCA induces the overexpression of HDAC6 and the resorption of cilia. Finally, in Specific Aim #3 we will evaluate the effect of cilia restoration on tumor cells. Our working hypothesis is that this intervention isa potential approach for decreasing cell growth and dedifferentiation of cholangiocarcinoma cells. The results of the present proposal will provide novel information regarding the ciliary-dependent mechanisms controlling the proliferation of tumor cells; and will provide the foundation for a plausible anti-cancer therapeutic treatment based on the rescue of primary cilia architecture and function.